The present invention relates to down hole tension/compression devices and more particularly to devices for use with battery powered self contained logging tools employed in oil well drilling operations.
A problem which arises in such operations is that when a logging tool is deployed on the end of drill pipe or coiled tubing. If the logging tool becomes stuck in the borehole there is no indication at the surface that this has occurred in contrast to a logging tool connected by cable to the surface where the movement or non-movement of the cable will indicate movement or non-movement of the logging tool.
In the event that a self-contained logging tool becomes stuck movement of the drill pipe can result in damage to the tool.
It is an object of the present invention to provide a down hole tension/compression device which provides an early warning of when a tool is shuck to enable drill pipe motion to be halted, thereby preventing damage to the tool.
The present invention therefore provides a self contained logging tool comprising apparatus for logging a well, said tool including normally open fluid flow valve means, said valve means being operable when the drill pipe moves with respect to the logging tool to close and to restrict flow of fluid through said valve to thereby restrict the flow of fluid within said drill pipe, thereby creating back pressure within said drill pipe to provide an indication at the surface that the logging tool is stuck.
The present invention also provides a valve for use in a logging tool, said valve comprising an inlet and an outlet for fluid flow, said outlet comprising first and second overlapping slot means, said first overlapping slot means being operable as movement increases to move relative to said second overlapping slot means to progressively restrict the flow of fluid through said valve.
The present invention also provides a down hole device including a valve means as described above and further including poppet valve means operative to be actuated at an excessive pressure to provide a bypass flow route for said fluid. The present invention further comprises a method of operating a logging tool comprising the steps of connecting said logging tool to the end of a drill pipe, lowering said logging tool, on the end of said drill pipe, into a drill hole; and pumping mud down said drill pipe, said mud flowing through said logging tool via valve means situated within said logging tool;
said method comprising the further steps of detecting when said logging tool becomes stuck in the drill hole by detecting restriction of mud flow in the drill pipe caused by operation of said valve means, and on detection of such restriction halting movement of said drill pipe in said drill hole.